1. Field of the Invention
The present invention concerns a device used to determine the flow rate of a medium, e.g. of a fluid or a gas, including a housing with a chamber through which the medium is flowing axially and which receives an impeller wheel with at least one blade, whereas the impeller wheel is provided with a carrier body having a centrical boring for receiving an axle, whereas the carrier body is provided in the area of the axle with at least one opening running radially to the centrical boring in the carrier body.
2. Description of the Prior Art
DE 41 11 001 discloses a device with a housing provided with an impeller wheel in a boring thereof which is brought to rotate. To induce the rotation of the impeller wheel, a so-called "spin body" is accomodated in front of the impeller wheel. This spin body occasions a spin within the flow, which in its turn brings the impeller wheel to rotate. To determine the rotation velocity, the blade ends are provided with magnets, whereas via said magnets a tension is induced in a spool accomodated in the housing. The rotation velocity of the blades can be determined by counting the tension pulses in the spool which are occasioned by the magnetic blades of the impeller wheel. This rotation velocity serves as a measure for the flow rate.
FR-A 2 717 536 discloses a device used to determine the revolutions/min. of a turbine, a perforated disk being accomodated in front of the turbine to equalize the incoming flow.
CH-PS 308922 discloses a flowmeter with a rotor, as it is used for measuring the volume of fluids. The rotor includes a carrier body with a pulse-inducing element designed as a magnet and cooperating with a corresponding spool in the housing of the flowmeter. Blades are moreover accomodated on the rear end of the carrier body, whereas the carrier body is located in the housing so as to be axially movable.
The device described in U.S. Pat. No. 5,372,048 shows a housing with an impeller wheel, whereas the impeller wheel is borne by an axle. Here too, the impeller wheel can be received by the axle so as to be axially movable. The impeller wheel itself has on its outer periphery a magnetic cage serving as pulse-inducer for a spool accomodated in the housing in order to determine the revolutions/min. of the rotor.
JP-A 56128414 discloses a turbine-shaped flowmeter where the rotor, provided with blades, is magnetically accomodated in the housing. The blades themselves are accomodated crosswise on the housing of the rotor.
JP 57020611 also shows a flowmeter whose rotor has two crosswise arranged blades, whereas a magnet is accomodated in their crossing point to serve as a pulse-inducer.
DE-A 34 15 366 discloses a water meter whose turbine wheel is radially flowed against. The bedding of the turbine wheel is assured by radial bearings on an axle, whereas the radial bearings are connected to a centrifugal chamber of the impeller wheel via a channel so that dirt particles are scavenged from the bearings by the water flow. This water meter is quite big in size because of the radial flow against it. In order to increase the pulse ratio of the counter and with it the exactitude of said counter, a transmitter is provided, increasing the size even more.
Another disadvantage of this counter is that it has to be installed horizontally in flow direction, since otherwise the wear in the area of the bearings is too high. It is also possible that, due to the guiding of the sluice, dirt particles in the water are flushed into the bearings, causing them to deteriorate faster. A reduction of wear is thus out of the question.
WO 92/21939 discloses a device of the type mentioned above. Here, two radially running borings for the impeller wheel are provided at the end of the axle in the carrier body, said borings being arranged opposite to one another in the carrier body. The function of the borings is to permit fluid to reach the area between axle and carrier body where it has to care for lubrication, cooling and scavenging. It is not conceivable that the fluid is entering both borings and is exiting at the opening of the axle boring in the carrier body. This cannot be since the flow resistance in the area between axle and carrier body is higher than the resistance provided by one of the afore-mentioned borings. It has therefore to be assumed that the fluid is entering the one radial boring and is exiting through the other radial boring. Even if appreciable quantities of fluid are reaching the area between the axle and the boring in the carrier body, the risk that dirt particles carried along by the water are reaching this area, causing thus a faster deterioration, is still given, since, in the end, the flow medium, for example water, will also carry considerable quantities of dirt particles.
Depending on the volume of flow, the impeller wheel proved to be able to reach up to 30,000 revolutions/min. Moreover, so many revolutions/min. are considerably warming up the location of the impeller wheel, due to the friction between the axle and the impeller wheel or the carrier body. This friction considerably wears the bearing of the impeller wheel.